The present invention relates generally to a vehicle lifting and towing apparatus and, more particularly, to an improved low profile vehicle lifting and towing device having a carriage slidable along an inclined column to orient a lifting boom along a vertical and horizontal path rearwardly from the towing vehicle.
Because newer automobiles are being produced with plastic bumpers, air foils and fender flares, and because of the ease of operation in a variety of towing conditions, there is an increased demand for wheel lift tow trucks. Today's wheel lift tow trucks typically use a lower or lifting boom upon which the wheel lift assemblies are mounted. The lifting boom is generally horizontally extendible and tiltable on a vertical arc which enables the disabled vehicle to be lifted from underneath the chassis by the wheels in a variety of situations. As a result, wheel lift tow trucks are now recognized to provide many advantages over conventional tow trucks using only overhead boom and sling arrangements.
Known lower boom lifting and towing assemblies fall into two general categories. One type has a lower boom which pivots about a stationary pivot point or is attached with a mechanical parallelogram linkage to a stationary frame member. Another type utilizes an inclined column which enables the lifting boom to move along the inclined column from a retracted position to an extended position downward and outward from the rear of the towing vehicle.
For example, the towing apparatus disclosed in U.S. Pat. No. 4,679,978 is a type which pivots the lower boom by the use of a parallelogram linkage about a stationary frame member. There are, however, several disadvantages associated with the lifting and towing apparatus of this type. Notably, because of the geometrical constraints of the parallelogram linkage, the maximum horizontal extension of the lifting boom from the rear of the towing vehicle is limited. Similarly, devices of this type have decreased arc of vertical tilt of the lifting boom. These deficiencies reduce the effectiveness of the operation of the apparatus under certain towing conditions. Further, when a device of this type is in its fully retracted position, the lifting boom (and associated wheel lift) protrudes out from the rear end of the towing vehicle further than desirable. Additionally, towing apparatus of this type have increased weight behind the centerline of the rear wheels of the towing vehicle which decreases the amount of weight that can actually be lifted before the front wheels of the towing vehicle start to lift off of the ground. In other words, these towing apparatus undesirably increase the tipping moment of the towing vehicle.
Another general category of lower boom lifting and towing assemblies is that disclosed in U.S. Pat. No. 4,634,337, which incorporates an inclined column arrangement. While overcoming some of the disadvantages of the above type of lifting and towing assembly, the design of this type has several drawbacks and disadvantages, produced in part as a result of the lifting cylinder being operably and directly connected to the lifting boom housing. In this configuration, the lifting cylinder is collinear with the housed within the inclined column. As a result, in order to achieve the desired range of vertical movement of the lifting boom, it is necessary to have the column protrude above the deck of the towing vehicle in a traditional deck situation (or, alternatively, having to enclose the inclined column in a raised deck). Because the column protrudes through or above the traditional deck, the movement of the upper boom is impeded at its lowermost position. This obstructs the driver's vision from the cab of the towing vehicle, which reduces the efficient operation or placement of the lifting boom from the cab of the towing vehicle, as well as reducing general driving safety. An like the devices utilizing a parallelogram linkage, devices of the known inclined column type also have increased weight behind the centerline of the rear wheel of the towing vehicle undesirably increasing the tipping movement of the towing vehicle.